This invention pertains to an induction heated casting channel or drain of a high temperature metal alloy fusing furnace or the like.
Superalloys are divided into three categories: austenitic steel and alloys which contain more than 20% of iron, basically comprised of iron, nickel, and chromium or iron, chromium, nickel, cobalt, and austenite, and alloys containing less than 20% of either nickel or cobalt based iron. Superalloys contain elements which can form carbides or intermetal phases: molybdenum, tungsten, vanadium, niobium, titanium, and aluminum. Their useful characteristics are their mechanical and chemical resistance at temperatures exceeding 900.degree. or 1,000.degree. C., and their flow resistance.
They are used to mold mechanical parts designed to resist high temperatures, such as parts for metallurgical furnaces, parts for the aeronautics, aerospace, and automobile industries, especially rotors for gas turbines or turbojet blades, exhaust valves, heating elements and maintenance teeth for industrial furnaces, tubular products for refineries in the oil industry, etc. Alloyed or low-alloy steel is used, among other things, for molding parts for the mechanical and building industries (building steel).
The casting channel for such an alloy can be that of a fusing furnace or else can be connected to a foundry casting ladle.
A metal alloy at high casting temperature solidifies quickly when there is a drop in temperature. In order to prevent such solidification, it is preferred to maintain the metal alloy inside the heated furnace as long as possible, making sure that it does not stagnate in the furnace casting drain or channel between two successive castings designed to fill a mold applied to the outlet orifice of the casting drain. For that reason, a rotating fusing furnace is used which tilts in order to empty the drain between two successive castings back inside the heated furnace by gravity flow.
An induction coil is also embedded inside the refractory lining of the casting drain, along its entire length, in order to induce a secondary heating current in the liquid alloy when it fills the drain just before and during a casting, thus reducing the chances of solidification of the molten alloy. Such a drain equipped with an embedded induction coil does not generate heat in the absence of liquid metal to serve as a secondary winding or core, however, such as between two successive castings when the drain is lifted to make the liquid metal alloy run back down into the furnace. The result is that, when casting resumes, a risk of initial solidification remains when the metal alloy enters the inadequately heated casting drain.
The problem thus exists to eliminate the cooling and solidification of a metal alloy at a casting temperature of at least 1,400.degree. C. inside a casting channel, between two successive castings of a mold, by heating the channel even when it does not contain any liquid metal. This problem could be solved, theoretically at least, by introducing inside the wall of the channel electric heating resistors, as is known. In practice, however, heating a casting channel with a Joule effect is difficult to achieve if not impossible; because of expansion it is difficult to embed a heating resistor inside a refractory fitting, and moreover it is difficult to couple a high intensity current to such an embedded resistor because of the high potential that is needed. For that reason induction heating is preferred since a properly cooled coil does not raise any expansion problems when it is embedded inside the refractory fitting, and the current coupling does not raise any problems, in spite of the powerful current potential required as a result of interposing an aperiodic generator between the channel coil and an electric current source.